This invention is related to the catalytic treatment in the presence of hydrogen of heavy hydrocarbon streams containing asphaltenic material, metals, nitrogen compounds, and sulfur compounds. More particularly, this invention relates to the hydroprocessing of hydrocarbon streams containing the aforesaid impurities in the presence of a multiple-catalyst system.
As the amount of heavier crude oil of poorer quality is required to be processed by refiners, processes that treat those hydrocarbon fractions containing increasingly higher levels of metals, asphaltenes, nitrogen, and sulfur will be employed.
It is widely known that various organometallic compounds and asphaltenes are present in petroleum crude oils and other heavy petroleum hydrocarbon streams, such as petroleum hydrocarbon residua, hydrocarbon streams derived from tar sands, and hydrocarbon streams derived from coal. The most common metals found in such hydrocarbon streams are nickel, vanadium, and iron. Such metals are very harmful to various petroleum refining operations, such as hydrocracking, hydrodesulfurization, and catalytic cracking. The metals and asphaltenes cause interstitial plugging of the catalyst bed and reduced catalyst life. The various metal deposits on a catalyst tend to poison or deactivate the catalyst. Furthermore, the asphaltenes tend to reduce the susceptibility of the hydrocarbons to desulfurization. If a catalyst, such as a desulfurization catalyst or a fluid cracking catalyst, is exposed to a hydrocarbon fraction that contains metals and asphaltenes, the catalyst will become deactivated rapidly and will be subject to premature removal from the particular reactor and replacement by a new catalyst.
Although processes for the hydrotreating of heavy hydrocarbon streams, including but not limited to heavy crudes, reduced crudes, and petroleum hydrocarbon residua, are known, the use of fixed-bed catalytic processes to convert such feedstocks without appreciable asphaltene precipitation and reactor plugging and with effective removal of metals and other contaminants, such as sulfur compounds and nitrogen compounds, is not too common. The catalysts of such processes generally have not been capable of maintaining satisfactory activity and performance. While the heavy portions of hydrocarbon streams once could be used as a low-quality fuel or as a source of asphaltic-type materials, the politics and economics of today require that such material be hydrotreated to remove environmental hazards therefrom and to obtain a greater proportion of usable products from such feeds.
Multiple-stage catalytic processes wherein a hydrocarbon stream having a high metals content is first subjected to a hydrodemetallization step followed by a hydrodesulfurization treatment are known. However, catalyst deactivation occurs quite rapidly and therefore prohibits such processes from providing suitable commercial application. Such multiple-stage catalytic processes are disclosed in U.S. Pat. Nos. 3,730,879 (Christman, et al.); 3,977,961 (Hamner); 3,985,684 (Arey, et al.); 4,016,067 (Fischer, et al.); and 3,928,176 (Hamner, et al.). The catalysts that are disclosed in the aforesaid patents contain a hydrogenating component that comprises one or more metals from Group VIB and/or Group VIII of the Periodic Table of Elements on a high-surface area support, such as alumina. Combinations of metals such as cobalt and molybdenum, nickel and molybdenum, nickel and tungsten, and cobalt, nickel, and molybdenum have been considered. In general, the preferred metals in such hydrotreatment processes are a combination of cobalt and molybdenum. Such is the case for the first-stage catalyst which is employed to remove a major portion of the contaminating metals and the second-stage catalyst, which is employed primarily to remove sulfur.
In U.S. Pat. No. 4,119,531, Hopkins, et al., disclose a catalyst for the hydrodemetallization of petroleum hydrocarbon streams containing asphaltenes and large quantities of metals, which catalyst consists essentially of a small amount of a single hydrogenation metal selected from Group VIB of the Periodic Table of Elements and metals from Group VIII of the Periodic Table of Elements deposed on a large-pore alumina. Suitably, nickel or molybdenum is employed as the hydrogenating metal. The catalyst is characterized by a surface area of at least 120 m.sup.2 /gm; a pore volume of at least 0.7 cc/gm, and an average pore diameter of at least 12.5 nm (125Angstrom units [.ANG.]).
In U.S. Pat. No. 4,181,602 and U.S. Pat. No. 4,188,284, Quick, et al., disclose processes for hydrotreating a heavy hydrocarbon stream containing metals, asphaltenes, nitrogen compounds, and sulfur compounds, wherein the stream is contacted with a catalyst comprising a hydrogenating component comprising chromium and molybdenum on a large-pore, catalytically active alumina. In U.S. Pat. No. 4,181,602, the hydrogenation component also comprises a small amount of cobalt. The catalysts possess a pore volume within the range of about 0.4 cc/gm to about 0.8 cc/gm, a surface area within the range of about 150 m.sup.2 /gm to about 300 m.sup.2 /gm, and an average pore diameter within the range of about 10 nm (100 .ANG.) to about 20 nm (200 .ANG.). The pore-size distribution of each of these catalysts is as follows: about 0% to about 10% of the pore volume is in pores having diameters that are smaller than 5 nm (50 .ANG.), about 30% to about 80% of the pore volume is in pores having diameters within the range of about 5 nm (50 .ANG.) to about 10 nm (100 .ANG.), about 10% to about 50% of the pore volume is in pores having diameters within the range of about 10 nm (100 .ANG.) to about 15 nm (150 .ANG.), and about 0% to about 10% of the pore volume is in pores having diameters that are larger than 15 nm (150 .ANG.).
In U.S. Pat. No. 4,212,729, Hensley, et al., disclose a two-stage catalytic process for the hydrodemetallization and hydrodesulfurization of a hydrocarbon feedstock containing asphaltenes and a substantial amount of metals, wherein said feedstock is contacted in a first catalyst zone with a catalyst comprising a hydrogenation metal component selected from the group consisting of a Group VIB metal, a Group VIII metal, and a mixture thereof and a porous inorganic oxide support, said catalyst having a surface area of about 120 m.sup.2 /gm to about 400 m.sup.2 /gm, a pore volume of about 0.7 cc/gm to about 1.5 cc/gm, and an average pore diameter within the range of about 12.5 nm (125 .ANG.) to about 35 nm (350 .ANG.). The effluent from this first catalyst zone is contacted subsequently with a catalyst consisting essentially of at least one active original hydrogenation metal selected from Group VIB deposed on a catalytically-active support comprising alumina, said catalyst having a surface area within the range of about 150 m.sup.2 /gm to about 300 m.sup.2 /gm and having a majority of its pore volume in pore diameters within the range of about 8 nm (80 .ANG.) to about 13 nm (130 .ANG.), and a pore volume within the range of about 0.4 cc/gm to about 0.9 cc/gm.
The disclosures of each of the last three patents are incorporated herein by reference.
Not one of the above-discussed references discloses a three-catalyst hydrotreating process wherein the last catalyst contains both chromium and molybdenum and the second catalyst contains only a Group VIB metal on a relatively small pore support material. There has now been found a process for the hydrotreating of heavy hydrocarbon streams containing asphaltenes and a substantial amount of metals, which process comprises contacting the stream in sequence with three catalysts. This process provides an improvement over the prior art processes by providing a lined-out deactivation rate that is very low.